1. Field of the Invention
The present invention relates to electrical and other types of connections that penetrate through the walls of an enclosure, wherein the enclosure may be maintained at atmospheric, sub-atmospheric or super-atmospheric pressure and/or in a chemically or electrochemically active state. In particular, the invention relates to feedthroughs in which a longitudinal biasing force both holds the feedthrough member in the enclosure wall and elastically seals the connection of the feedthrough through the enclosure wall.
2. Background of the Prior Art
A feedthrough is used to pass a conductor, a conduit, or other member through an aperture in the wall of an enclosure such as a semiconductor processing chamber. The feedthrough must be capable of withstanding chemically or electrochemically corrosive and/or explosive environments which may be maintained within the enclosure, while simultaneously sealing the aperture to maintain the isolation of the enclosure from the environment and prevent leakage of any corrosive or explosive materials therethrough. Additionally, where the feedthrough is supplying an electric current into the enclosure, the conductive portion of the feedthrough must not touch the wall of the enclosure or aperture. The enclosure wall is typically maintained at ground potential, and, if the conductive portion of the feedthrough does touch the wall it will short to ground. Further, in some applications the enclosure wall may be maintained at a high voltage. In that instance, if the conductive portion of the feedthrough touches the wall of the enclosure or aperture, the internal componentry being fed by the feedthrough will receive an electrical overload.
In one known method of providing an electrical feedthrough, a conductor such as a wire is held through the enclosure aperture, and a molten glass or ceramic potting material is poured into the aperture around the conductor. When the molten material hardens, it forms a sealing mass around the conductor within the aperture. Glass or ceramic potting materials are used in many feedthrough applications because they have high electrical insulative properties and are relatively impervious to the processing environments maintained within the enclosure. As a result, they maintain their sealing integrity through thousands of processing cycles. However, the glass or ceramic-based feedthrough has several disadvantages. First, the conductor of the feedthrough, such as the aforementioned wire, must be maintained in a specific location within the aperture while the molten material is formed around the conductor. If the conductor alignment through the aperture is disturbed as the feedthrough seal is formed and the conductor contacts the side of the aperture, the feedthrough will short to ground in the case of a grounded enclosure, or feed a surge current into the enclosure where the enclosure wall is maintained at a high voltage. Further, the final dimensions of the glass and ceramic materials are difficult to control, and protrusions of these insulating materials may form around the aperture and prevent the placing of componentry directly adjacent to the entry of the aperture into the enclosure. Additionally, the conductor or conductors passing through the glass or ceramic body must be connected to a circuit after the feedthrough is created, most commonly by soldering. It has been found that in some applications, particularly where the internal component being fed by the feedthrough is a delicate member such as a printed circuit board, the soldering of the conductor to the internal apparatus may lead to failure of the internal component.
The processing of the glass or ceramic to form the body of the feedthrough also limits the types of connections which can be made with the feedthrough. The melting temperature of the glass and ceramic sealing materials limits their use to feedthroughs having metallic or other conductors with high melting temperatures. Also, if a glass or ceramic feedthrough fails, an equipment user must have the capability to melt glass or ceramic and pour it in place to recreate the feedthrough, or must remove the equipment to a shop where a new feedthrough can be fabricated in the aperture. Both options are expensive and time consuming. Finally, where the enclosure is heated or cooled, the differential rates of expansion between the enclosure material and the glass or ceramic material can lead to leakage or failure of the feedthrough.
One alternative to forming the feedthrough by pouring a molten glass or ceramic around a solid conductor is to first create a ceramic or glass body in the aperture, and then form the conductor through the body. However, to obtain desirable sealing characteristics the ceramic or glass body must be formed in the aperture from a molten glass or ceramic potting material, and the conductor must be formed from a molten conductive material poured through a secondary aperture in the body. The secondary aperture may be formed as the body is formed, or, the secondary aperture may be drilled through the solidified body. The need to melt and pour the conductive material and the glass or ceramic potting material makes these feedthroughs as difficult to form and replace as those formed by pouring the molten glass or ceramic around a solid conductor.
In some processing environments, epoxy or other adhesives may be used in place of glass or ceramic to form the body of the feedthrough. These materials overcome the problems associated with forming high temperature molten materials in the aperture to create the feedthrough. However, a conductor may still come into contact with the enclosure wall as this type of feedthrough is formed, and the epoxy or adhesive materials will also form material protrusions around the entry of the aperture into the enclosure and thus prevent the placement of componentry directly adjacent to the entry of the aperture into the enclosure.